The present invention is directed to a method for inspecting the neck portion of containers such as bottles in a bottle manufacturing or filling line, particularly, the lip surface on the neck portion of a bottle. The invention more specifically concerns such a method which can readily be automated.
Conventionally, inspection of bottle lips was primarily carried out by visual inspection. However, it is impossible to accurately visually detect fine defects, and the productivity rate when visual inspection is employed is rather low.
To automate the inspection process, Japanese Examined Patent Publication No. Hei-5-40846 discloses an automated image sensor wherein light reflected from the entire area of the lip surface of the bottle is received by the sensor, and the resulting signal produced by the sensor is compared with a reference value. When the signal is greater than the reference value, the bottle is Judged as having a defect in the lip surface. When this occurs, the peak angle formed by the defect is determined from the ratio of the maximum depth of the defect to the width of the defect. When the angle is less than a certain value, the depth and width of the defect are calculated, and if the depth and width are greater than the reference value, the bottle is judged to be defective.
However, it is difficult to detect certain types of defects, for example, a dimple (FIG. 5(a)), an edge cut (FIG. 7(a)), or a blister or a line surface (FIG. 8(a)) etc., using the method disclosed in Japanese Examined Patent Publication No. Hei-5-40846 in cases where the depth and width of the defects are small. Further, since the method involves receiving light reflected from the entire area of the lip surface, it is necessary to obtain very stable light levels. Therefore, the conventional method has low reliability albeit at a high cost.